How To Improve Bolt Joint Strength?
The strength of the bolt joints mainly depends on the strength of the bolt. There are many factors affecting bolt strength, such as structure, size parameter, assembly process, material, manufacturing precision grade, and so on. So how can we strengthen the bolt joint? As a professional fastener manufacturer, Xinchi fastener Company is happy to answer this question for you. We can improve the strength of the bolt joint from the following aspects.
Improve the fatigue strength of bolts
It has been proved by theory and practice that the fatigue strength of bolts can be improved by decreasing the stiffness of bolts or increasing the stiffness of the connected parts when the working load and residual preload remain the same. But the preload should be increased appropriately to ensure the tightness of the joint. The commonly used measures to reduce bolt stiffness include increasing bolt length, reducing bolt rod diameter, or making hollow structure flexible bolts. Flexible bolts have large deformation and strong energy absorption during stress and are also suitable for bearing impact and vibration. If the elastic element is installed under the nut, when the working load is transmitted from the connected part, due to the larger deformation of the elastic element, it can also play the effect of the flexible bolt. In order to increase the stiffness of the connected parts, it is not suitable to use a small stiffness gasket. It is better to use sealing rings for tight connections.
Improve the load distribution between thread
When ordinary nuts are used, the axial load is distributed unevenly among the turns of the screw threads. From the surface of the nut-bearing, the load is maximum in the first ring and decreases in subsequent rings. Theoretical analysis and experiments show that the more the number of turns, the more uneven the load distribution is, and the thread after the 8th ~ 10th turn is almost free from load. Therefore, using thick nuts with many turns can not improve the connection strength. If the suspension (tension) nut is used, the conical suspension section of the nut and the bolt rod are tensile deformations, which helps to reduce the difference in pitch between the nut and the bolt rod, so that the load distribution is more uniform.
Reduce stress concentration
The root and end of the thread, the joint of the bolt head, and the bolt rod, all have stress concentration, which is the dangerous part of fracture. Especially at the root of the screw thread, because the rod is stretched, the thread is bent and cut, and the force is uneven, the situation is more serious. The fatigue strength of bolts can be increased by 20%~40% by increasing the radius of the thread root fillet to reduce stress concentration. Good results can be obtained by using the retracting groove at the end of the thread and keeping the thread within the bearing surface of the nut. The newly developed MJ bolt is used for aerospace and spacecraft bolts, and its main structural characteristic is that the radius of the thread root fillet is enlarged.
High-strength steel bolts are sensitive to stress concentration, but the results are favorable because they can be tightened with greater preload and higher ultimate strength.
Adopt a reasonable manufacturing process
Manufacturing technology has a great influence on the fatigue strength of bolts. Due to the effect of cold work hardening, the residual compressive stress on the surface of the bolts with grinding thread and there is a reasonable metal flow line, so the fatigue strength of the bolts with grinding thread is 30%~40% higher than that with turning thread. The effect of rolling after heat treatment is better. In addition, nitrocarburizing, nitriding, and shot blasts can improve the fatigue strength of bolts.
Anji Xinchi Fastening Piece Co., Ltd is a trustworthy fastener company, especially in furniture nuts. And we are the designated fastener supplier to“STAPLE”. As a trusted fastener supplier, Xinchi Fastener Company can offer a wide range of high-quality fasteners, including tee nuts, screws, bolts, rivets, washers, etc. If you want to know more about fasteners or want to wholesale fasteners, please feel free to contact us. And then our experienced and expert service team will reply to you as soon as possible.